How the Human Body Works: An Overview of the Organ Systems

The human body is comprised of cells, tissues and organs.

  • The cell is the basic living unit of all organisms. Epithelial tissues, muscles, nerves, and connective tissues are the four basic cell types of the human body.
  • Tissues are groups of cells that work together to form a multicellular organism- for example skin or heart tissue.
  • An organ is a group of tissues which constitute a distinct structural and functional unit- for example the liver or kidney.

Organization of the body

The human body is an incredible machine that is made up of a variety of systems. These systems work together to keep us alive and functioning.

The highest level of body organization is that by organ system- composed of all four tissues (heart, blood vessels, blood cells).

There are nine major organ systems in the human body: integumentary (skin), musculoskeletal (bones), respiratory (lungs), digestive (stomach), circulatory (heart), urinary (kidney/ureters), endocrine (glands), reproductive (sex organs) nervous system(brain/spinal cord).

Heart and Circulatory system

The heart is one of the most important muscles in the human body. It is responsible for pumping blood throughout the body, and it is one of the strongest muscles in the human body. The heart is a four-chambered organ that sits in the middle of your chest.

The human heart is homologous with other vertebrate hearts. This means that the structure and function of your heart is very similar to other animals, such as dogs and cats.

There are three types of circulation: systemic, pulmonary, and coronary.

  • Systemic circulation occurs when blood leaves the left ventricle and enters into general circulation. This type of circulation supplies all organs except for those in the lungs (pulmonary circulation).
  • Pulmonary circulation occurs when blood from systemic circulation enters into capillaries located in the lungs. In this case, oxygenated blood returns to the left atrium and then pumped out to systemic circulation.
  • Coronary Circulation is a third type of circulatory system that is specific to coronary arteries which supply blood to your heart muscle (myocardium). When these arteries become blocked or narrowed, it can lead to a heart attack.

Blood is connective tissue that helps transport essential nutrients and minerals throughout your body. Blood also contains white blood cells which help fight infection, as well as red blood cells which carry oxygen throughout your body. Blood has a semi-permeable membrane which allows for easy absorption of nutrients while preventing waste from exiting the blood vessels too quickly.

Respiratory system

The respiratory system is made up of the lungs and occurs in cycles. The process begins with inhalation and ends with exhalation. In humans, the respiratory system is responsible for taking in oxygen and releasing carbon dioxide.

The respiratory system is comprised of the trachea, bronchi and lungs. Diffusion occurs through alveoli in the lungs, which are air sacs. The lung’s job is to move air around our bodies so we can breathe it in or out of our lungs depending on what our needs are at that time

Digestive system

The digestive system is a series of organs that work together to break down food and extract nutrients for the body to use. The major organs in the digestive system are: mouth, teeth, tongue, oesophagus, stomach, liver, pancreas, small intestines and large intestines.

The mouth is where food begins to be broken down. Teeth chew food into smaller pieces and the tongue helps mix it with saliva which contains enzymes that start the digestion process. The oesophagus carries food from the mouth to the stomach. The stomach secretes strong acids and powerful enzymes to break down food into a liquid form. The small intestine is the site of nutrient absorption. Nutrients pass through the intestinal wall and into the bloodstream. The large intestine is the final stop for stool. The large intestine transforms it from liquid to solid as water is removed. Solid waste passes out of the body through the anus via anal sphincters muscles.

Skeletal system

The skeletal system is the body’s framework. It includes bones, muscles, cartilage and ligaments. The 206 bones in the human body produce blood cells. Bones also store minerals such as calcium and phosphorus.

Bones are connected by muscles, which attach to the bone by tendons. Muscles contract when they receive a signal from the brain or spinal cord. This movement is what allows us to move our limbs and organs. Cartilage is a tough but flexible connective tissue that covers the ends of bones where they meet each other (articulations). Ligaments are strong bands of connective tissue that hold bones together at joints.

The musculoskeletal system provides structure, protection and movement to the body. It is made up of skeletal muscle cells, which are attached to bones by tendons. These cells contain myofibrils with contractile fibers that can shorten and lengthen in response to a signal from the brain or spinal cord

Muscular system

The muscular system is made up of over 600 muscles in the human body! It is the second largest system after the skeletal system.

The muscular system is responsible for movement, posture and generating heat in the body. There are three types of muscles: skeletal, cardiac and smooth.

  • Skeletal muscles are attached to the skeleton and are used to move the bones. They are voluntary muscles, which means that we can control them consciously.
  • Cardiac muscles are found in the heart and contract rhythmically to pump blood around the body.
  • Smooth muscles are found in organs such as the stomach, intestines and bladder, and they involuntarily contract to push food through digestion or urine through urination.

Nervous system

The nervous system is a crucial part of the human body. It consists of two different systems: the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord, while the peripheral nervous system includes all of the nerves outside of those two areas.

Every part of our bodies is connected to the central nervous system through neurons- nerve cells. These connections allow us to control every aspect of our bodies, from movement to emotion. The autonomic nerve functions are also attached to the forebrain- including sexual development and emotion functions.

The hindbrain consists of three parts: medulla, pons, and cerebellum. Together, these areas control things like heart rate, breathing, and digestion.

The somatic nervous system transmits motor and sensory impulses from CNS back to body and limbs- this allows us to avoid life-threatening accidents or responses to abnormal conditions.

Finally, the autonomic nervous system prepares our bodies for violent attacks or abnormal conditions such as a fever or post-exercise state.

Female reproductive system

The female reproductive system is responsible for the production of eggs and the regulation of hormones. It also includes the organs that carry the baby during pregnancy and birth.

The external parts of the female reproductive system are called the vulva, which includes the clitoris, labia, and mons pubis.

The internal organs of the female reproductive system are located in the pelvis. They include:

  • Vagina: a muscular tube that leads from outside of the body to the uterus
  • Cervix: a narrow passage that connects the vagina to uterus
  • Uterus: a pear-shaped organ where babies grow
  • Fallopian tubes: two thin tubes that lead from each side of the uterus to an ovary
  • Ovaries: two almond-sized organs located on either side of the uterus that produce eggs

Male reproductive system

The reproductive system is the group of organs in a male that help in reproduction. The primary organ is the testes, which produce sperm. The sperm travel through a series of tubes called the vas deferens to the prostate gland and seminal vesicles. These glands add fluid to the sperm to create semen. The penis ejaculates semen when stimulated sexually.

The reproductive system includes:

  • Testes produce sperm cells, while the epididymis takes care of storing sperm cells.
  • Penis is the male organ for sexual intercourse. Semen, which contains sperm, is expelled through the end of the penis when a man reaches sexual climax.
  • Prostate gland produces seminal fluid, which is mixed with sperm.
  • Seminal vesicles produce a thick, viscous fluid called seminal plasma.
  • Urethra: the tube that carries urine from the bladder to outside of body.

Frequently Asked Questions on the Human Body

How many muscles are in the human body?

There are over 600 muscles in the human body. Muscles can be classified into three categories: skeletal, cardiac, and smooth.

How many bones are in the human body?

The human body has 206 bones. These bones are divided into two categories: movable and immovable. The movable bones are those that make up the limbs of the body – arms, legs, etc. Immovable bones are those that make up the skull and spine.

What is a normal human body temperature?

The average core body temperature of a human is 98.6 degrees Fahrenheit (37 degrees Celsius). However, it has fallen since the Industrial Revolution in the United States. A decrease in body temperature is related to a decrease in resting metabolic rate, which leads to a reduction of overall energy expenditure.

How much water is in the human body?

The human body is made up of water and organic compounds. Of the body’s total weight (which averages 60% of lipids, proteins and phospholipids), water accounts for two-thirds of it. Humans have little structural carbohydrate in their bodies, unlike plants and other invertebrate animals.